Various water filtration systems designed for residential and commercial use have become increasingly popular for the removal of unwanted substances from input water. Filtration systems utilize a filter module such as a reverse osmosis filter module to provide filtered output water for consumption or other use.
Two common water filtration systems are air-on-water systems that discharge product water into an enclosed pressure vessel against back pressure created by an air compartment within the vessel, and water-on-water systems that discharge product water into an enclosed pressure vessel and into a flexible water compartment that can be compressed by a separate source of water to remove the product water from the vessel.
In air-on-water systems, the water storage tank is divided into two compartments. The first compartment is for holding product water and the second compartment is filled with a pre-charge of air. As the filtration system produces water and fills the storage tank, the air compartment is compressed to accommodate the volume of product water introduced into the product compartment, which increases the air pressure. That increase in air pressure continues to rise for every ounce of product water forced into the storage tank. As such, air-on-water systems are subject to the back pressure of the air compartment, which causes the pressure differential across the filtering portion of the system to be reduced. This reduction in pressure differential thereby reduces the quality and quantity of filtered product water made in a given time. Product water quality particularly suffers if the product water is frequently drawn off and replaced in small quantities, as typically occurs in household systems. Moreover, an air-on-water system does not provide a constant flow rate of product water because the air compartment gradually loses pressure as the air compartment-propelled water is emptied from the storage vessel.
Water-on-water systems can address many of the shortcomings of air-on-water systems. Water-on-water systems typically include a pressure vessel containing two water-filled compartments. Often, a first compartment stores product water and a second compartment contains “squeeze” water. A physical separation between the compartments is movable or flexible so that water pressure in the first compartment is influenced by the water pressure in the second compartment. Thus, pressure from the “squeeze” side can discharge water from the product side to a faucet or other outlet downstream when there is a water demand. The physical separation between the compartments can be a membrane or other similar structure. In these water-on-water systems, there is only a small amount of backpressure acting upon the membrane, which is the amount of pressure required to force water from the squeeze compartment to the drain as the product compartment is filled.
There is a continuing need for improved water-on-water valves and filtration systems using such valves.